The present invention relates generally to high temperature measurement of materials or processes in vessels, and more particularly to an apparatus which continuously measures the temperature of material contained in a refractory vessel.
Vessels handling molten metals, such as BOF steel furnaces, are usually provided with a refractory lining to prevent the molten metal contents of the vessel from coming in contact with the outer supporting structure of the vessel. This lining can be made from bricks, poured as a casting, or from plastic refractory materials. Bricks are typically cut to fit the vessel and mortared into place. Forming the lining from castable materials is performed by lining the vessel with a form, and pouring the castable into the form. Plastic refractories are like thick castable materials, and have the consistency of modeling clay. They are installed by ramming or pounding the material in place, and then setting into a monolithic lining by firing. Over a period of time, the refractory lining of the refractory erodes, and portions become damaged, reducing the thickness. This erosion is due in large part to overheating of the molten metal contained in the vessel.
Temperature measurement of molten metal in such vessels is typically accomplished by using an infra-red temperature device, or by temporarily inserting a standard thermocouple into the molten bath. Infra-red devices only measure the surface temperature of the molten metal, and when the surface starts to cool and form a crust, this method is no longer suitable. At this point, temperature is measured by breaking the surface crust and inserting a temperature probe or thermocouple, into the metal bath.
Due to the hostile environment encountered in industrial applications, the thermocouple is usually placed within a protecting tube, or thermowell. Typically, rod-shaped thermowells of various lengths containing thermocouples are employed to measure the temperature of the metal bath. The thermowell can be manufactured from various materials depending on the intended temperature range expected to be measured. For measurement of lower temperatures (up to about 1400.degree. F.), thermowells of stainless steel can be used. As the temperature goes up (to about 4000.degree. F.), refractory coated thermowells, or solid refractory thermowells, must be used. These are typically rod-shaped, and six inches to two feet in length. Such thermowells are not suited for continuous service, and are essentially disposable. At high temperatures the refractory, or the steel under the refractory, loses its strength and breaks or erodes.
Rod-shape probes are inserted into the vessel through a hole drilled through the refractory lining. The hole in the refractory lining communicates with an opening in the vessel wall which permits passage of the thermocouple wire pair for connection with an appropriate temperature display. Thus, a problem associated with rod-shaped probes is that they provide a discontinuity through the entire thickness of the lining and the vessel. This produces a point of wear and potential point for failure of the lining.
Another type of thermowell consists of a bare thermocouple junction covered by a thin glass tube. These have a fast response time in that temperature is displayed rapidly, but are very short lived, burning out after only one or two measurements. Accordingly, it is an object of this invention to provide an apparatus capable of continuous, high temperature measurement of the molten materials contained in refractory lined vessels.
Another object of the invention is to provide a more accurate indication of temperature in a refractory lined vessel containing molten metal such that overheating of the molten metal is prevented.
Yet another object of the present invention is to minimize erosion of the refractory lining of a vessel containing molten metal by providing accurate temperature measurements to prevent overheating.
A further object of this invention is to provide a thermowell integral with the refractory lining of a vessel to eliminate discontinuities in the refractory lining caused by the use of rod-shaped thermowells.